Logs: freenode/#haskell
| 2020-10-13 11:43:48 | <kuribas> | Uniaika: although I think your case match is a good way BTW... |
| 2020-10-13 11:44:00 | <kuribas> | because it clearly shows you want exclusive or. |
| 2020-10-13 11:44:05 | <merijn> | Anyone know how to avoid "redundant import" warnings for "Data.Monoid ((<>))" on GHC >8.2 in a way that doesn't break GHC 8.0-8.2 |
| 2020-10-13 11:44:22 | <Uniaika> | merijn: I'm going to say the bad word but… |
| 2020-10-13 11:44:23 | <Uniaika> | CPP? |
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| 2020-10-13 11:49:02 | <kuribas> | CPP :) |
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| 2020-10-13 12:06:58 | hackage | termonad 4.0.1.1 - Terminal emulator configurable in Haskell https://hackage.haskell.org/package/termonad-4.0.1.1 (cdepillabout) |
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| 2020-10-13 12:09:20 | <merijn> | I just got rid of all the CPP :( |
| 2020-10-13 12:10:47 | <Uniaika> | I know, I know… |
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| 2020-10-13 12:13:43 | <merijn> | hmm, a change in examples probably doesn't warrant a new release |
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| 2020-10-13 12:16:51 | <kuribas> | merijn: do you know a better way to deal with breaking changes? |
| 2020-10-13 12:16:56 | <kuribas> | like the semigroup stuff |
| 2020-10-13 12:17:08 | <merijn> | kuribas: There's usually a migration guide with GHC |
| 2020-10-13 12:17:19 | <kuribas> | merijn: which recommends cpp... |
| 2020-10-13 12:17:36 | <merijn> | And the rule is that backwards compat for 3 releases should be possible without CPP |
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| 2020-10-13 12:22:56 | <hekkaidekapus> | dminuoso: After some light sleuthing, the OutsideIn algorithm seems to be implemented as described in the paper, more or less. I would succinctly answer this to your original question: no matter how involved a method’s constraints are, the solving will boil down to generating implicits and using them as evidence. |
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| 2020-10-13 12:25:38 | <dminuoso> | hekkaidekapus: Fair enough, the reason Im asking is, Ive been staring at a mail on haskell-cafe for so long, Im starting to think there's a bug in the instance selection algorithm. |
| 2020-10-13 12:26:19 | <dminuoso> | Where GHC selects an instance despite overlapping instances existing. |
| 2020-10-13 12:26:53 | <dminuoso> | The video though I think helped, since it explained roughly how the constraint checking on instances with context works. |
| 2020-10-13 12:27:00 | <tomjaguarpaw> | dminuoso: The Wrapper (Maybe a) mail? |
| 2020-10-13 12:27:03 | <dminuoso> | tomjaguarpaw: Yeah. |
| 2020-10-13 12:27:09 | <tomjaguarpaw> | I was also puzzled by that. |
| 2020-10-13 12:27:27 | <hekkaidekapus> | dminuoso, tomjaguarpaw: link? |
| 2020-10-13 12:28:21 | <tomjaguarpaw> | https://mail.haskell.org/pipermail/haskell-cafe/2020-October/132815.html |
| 2020-10-13 12:28:28 | <hekkaidekapus> | Thanks. |
| 2020-10-13 12:28:58 | hackage | hwk 0.5 - Commandline text processing with Haskell functions https://hackage.haskell.org/package/hwk-0.5 (JensPetersen) |
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| 2020-10-13 12:32:02 | <dminuoso> | % newtype Foo = Foo Int; instance {-# OVERLAPS #-} Show (Maybe Foo) where show _ = "foo" |
| 2020-10-13 12:32:03 | <yahb> | dminuoso: |
| 2020-10-13 12:32:10 | <dminuoso> | % newtype W a = W (Maybe a); instance Show a => Show (W a) where show (W a) = show a |
| 2020-10-13 12:32:11 | <yahb> | dminuoso: |
| 2020-10-13 12:32:14 | <dminuoso> | % foo :: Show a => W a -> String; foo a = show a |
| 2020-10-13 12:32:14 | <yahb> | dminuoso: |
| 2020-10-13 12:32:16 | <dminuoso> | This should be rejected. |
| 2020-10-13 12:32:28 | <dminuoso> | (Unless IncoherentInstances was enabled) |
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| 2020-10-13 12:33:42 | <dminuoso> | % foo' :: Show a => Maybe a -> String; foo' a = show a |
| 2020-10-13 12:33:43 | <yahb> | dminuoso: ; <interactive>:9:47: error:; * Overlapping instances for Show (Maybe a) arising from a use of `show'; Matching instances:; instance Show a => Show (Maybe a) -- Defined in `GHC.Show'; instance [overlap ok] [safe] Show (Maybe Foo) -- Defined at <interactive>:5:50; instance [overlap ok] [safe] Show (Maybe Ghci4.Foo) -- Defined at <interactive>:1:50; (The choice depen |
| 2020-10-13 12:33:47 | ← | JordiGH parts (jordi@octave/developer/JordiGH) () |
| 2020-10-13 12:34:01 | <ClaudiusMaximus> | % foo (W Nothing) -- just checking what happens at point of use |
| 2020-10-13 12:34:01 | <yahb> | ClaudiusMaximus: "Nothing" |
| 2020-10-13 12:35:37 | <ClaudiusMaximus> | % foo (W (Just (Foo 1))) -- just checking what happens at point of use |
| 2020-10-13 12:35:38 | <yahb> | ClaudiusMaximus: ; <interactive>:11:1: error:; * No instance for (Show Foo) arising from a use of `foo'; * In the expression: foo (W (Just (Foo 1))); In an equation for `it': it = foo (W (Just (Foo 1))) |
| 2020-10-13 12:35:45 | <dminuoso> | It seems, that the deferring the constraint `Show (Maybe a)` changes how instance is selected. |
| 2020-10-13 12:36:32 | <dminuoso> | If that was the case, it could imply that GHC falsely generates incoherent code. |
| 2020-10-13 12:37:12 | <dminuoso> | I tried debugging the type checker with a minimal program, but -ddump-tc-trace generated 5k lines of output.. |
| 2020-10-13 12:37:20 | <dminuoso> | The manual did *not* lie when it said it would be real chatty. |
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| 2020-10-13 12:38:30 | <dminuoso> | I think, if nobody else does it, Ill file a bug report. Either the GHC manual is incorrect, or GHC is buggy. One has to be the case here. |
| 2020-10-13 12:38:57 | <merijn> | Time for everyone's daily reminder of the invaluable service of packdeps having an RSS feed when you need to bump your package bounds ;) |
| 2020-10-13 12:39:38 | <merijn> | dminuoso: pfft, you're missing an alternative |
| 2020-10-13 12:39:43 | <merijn> | dminuoso: They could *both* be wrong :p |
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